There is a significant worldwide shortage of experimental phase diagram data at intermediate temperatures (around 600ºC to 900ºC for Fe-based and Ni-based alloys) where most alloys are used in service. This shortage results in large uncertainty of thermodynamic data and thus inability to accurately predict phase stability and driving force for phase transformations during materials processing and usage at this temperature range. The proposed study will develop a novel dual-anneal diffusion-multiple approach for high-efficiency determination of intermediate temperature phase diagrams and will apply the methodology to the Fe-Co-Cr-Mo-Ni system. A high-temperature (e.g. 1200 ºC) anneal of diffusion multiples will first create wide composition regions of solid solutions and intermediate compounds, which is equivalent to making many alloy compositions simultaneously. A subsequent intermediate temperature (e.g. 600 ºC) anneal will induce precipitation and formation of equilibrium phases, which is equivalent to the heat treatment of many individual alloys at a temperature of interest for phase diagram determination. The effective methodology to be developed here will have an impact on the design and long-term stability prediction of materials. Wide application of this method will lead to large amounts of phase equilibrium data for accurate assessment of the Gibbs energy functions to enable high-fidelity thermodynamic predictions at intermediate temperatures. High-fidelity prediction can reduce or eliminate the long-term thermal exposure experiments that are required now to test an alloy's propensity to detrimental phase formation or to promote stable precipitate phases to strengthen alloys, thus reducing the alloy design iterations and increasing the speed of new alloy design. The proposed study will also provide intermediate temperature isothermal sections of several ternary systems that are very important for the development of precipitation-strengthened stainless steels and Ni-based superalloys.
NON-TECHNICAL SUMMARY
There is a significant worldwide shortage of phase diagrams at intermediate temperatures (around 600ºC to 900ºC for steels and Ni-based alloys). This shortage of phase diagrams (which are maps for materials scientists to design alloys) leads to inability to accurately predict alloy behaviors at this critical temperature range where most alloys are used in service. The proposed study will develop a novel dual-anneal diffusion-multiple approach for high-efficiency determination of intermediate temperature phase diagrams. The effective methodology will have an impact on the design and long-term stability prediction of alloys. Wide application of this method will lead to large amounts of phase diagrams to enable high-fidelity prediction which can be used to eliminate the long-term thermal exposure experiments that are required now to test alloys' propensity to detrimental phase formation, thus increasing the speed of new alloy design. The timely design and insertion of high-performance alloys are critical to the global competitiveness of U.S. industries. This NSF program will also educate next-generation materials scientists with the advanced experimental tools so they can better serve the industry.
